Biodiesel production by methanolysis of waste lard from piglet roasting over quicklime

Waste lard from piglet roasting and quicklime (basically CaO) as a priceless fatty feedstock and a cheap solid catalyst, respectively were tested for the biodiesel production by methanolysis in a batch stirred reactor at moderate reaction temperatures (40-60 °C) for the kinetic study. For comparison, unheated and heated pork lards, as well as pure CaO, were also included in this study. The mass transfer limitation was observed in the initial period of all methanolysis reactions. The kinetic model combining the changing- and first-order reaction rate laws with respect to triacylglycerols and fatty acid methyl esters (FAMEs), respectively was verified for all three lardy feedstocks and both catalysts. The catalytic activity of quicklime was the same as that of pure CaO. The activation energy was demonstrated to be independent of the feedstock and the catalyst (59.1 ± 0.6 kJ/mol), but the waste lard reacted faster than the unheated and heated pork lards. At the methanol-to-lard molar ratio of 6:1, the catalyst amount of 5% (based on the lard weight) and the reaction temperature of 60 °C, a high FAME concentration in the final ester products (97.5%) within 60 min were achieved with the waste lard and quicklime in two consecutive batches. The same kinetic model was applicable in a continuous packed-bed tubular reactor filled with quicklime bits (2.0-3.15 mm) at the methanol-to-waste lard molar ratio of 6:1, the reaction temperature of 60 °C and the residence time of 1 h. Under these conditions, the biodiesel yield was 97.6%, while the FAME concentration in the biodiesel product was 96.5%.